1. Field of the Invention
The present invention relates to an ultrasonic probe for transmitting and receiving ultrasonic waves.
2. Description of the Related Art
The ultrasonic diagnostic apparatuses are broadly used in the field of medicine, which are to examine the internal body of a subject by transmitting an ultrasonic wave into a subject and receiving a reflected echo.
Recently, there is realized an ultrasonic probe capable of scanning three-dimensionally an ultrasonic wave by focusing and scanning of an ultrasonic beam in every direction, together with an ultrasonic diagnostic apparatus that generates and displays a stereoscopic (three dimensional) ultrasonic image based on the ultrasonic information, of from the examination subject, gathered by the ultrasonic probe.
FIG. 8 is a perspective view showing a construction of the existing ultrasonic transducer unit 10. The-ultrasonic probe has a plurality of transducers arranged in a two-dimensional form, as described in JP-A-2001-292496, for example. The two-dimensional-array-type ultrasonic probe realizes fast, three-dimensional scanning.
The ultrasonic transducer unit 110, incorporated in a two-dimensional-array-type ultrasonic probe, has acoustic matching layers 112, 113, ground electrodes (referred also to as common electrodes) 114, piezoelectric elements 116, signal electrodes (referred also to as discrete electrodes) 115, backing members 120 and boards 118, as shown in FIG. 8. The board 18 is printed with signal lines 22. Incidentally, the piezoelectric element 116, formed with a ground electrode 114 and signal electrodes 115, is referred to as an ultrasonic transducer (hereinafter, referred merely to as a transducer) 117.
The acoustic matching layers 112, 113 are provided in front of the transducer 117. The acoustic matching layers 112, 113 are to take a matching of between the transducers 117 and the subject.
The ground electrode 114 is formed at an end face of the transducer 117. The piezoelectric element 116 typically is formed of a binary or ternary piezoelectric ceramic. Consequently, the ground electrode 114 and the acoustic matching layers 112, 113 are connected in the order on one end (closer to the subject) of each of the transducers 117 arranged in a two-dimensional array form. The other end is connected with the signal line 112 that is to apply an electric signal for voltage application for piezoelectric effect and generating an electric signal based on an ultrasonic wave received from the subject. The two-dimensional arrangement of the transducers 117 allows for focusing of an ultrasonic wave in every direction and fast, three-dimensional scanning thereof.
The backing member 120 is provided in back of the transducer 117. The backing member 120 mechanically supports the transducers 117 or to absorb backward ultrasonic waves. The backing member 120 is to regulate the movement of the transducers 117 in order to shorten the ultrasonic pulse. The thickness of the backing member 120 is assumed having a sufficient thickness relative to (thickness for sufficient damping) the wavelength of an ultrasonic frequency to use, in order to keep well the acoustic characteristic of the ultrasonic transducer.
The board 118 is printed with a plurality of signal lines 122. The plurality of signal lines 122 correspond respectively to the signal electrodes 115 of the plurality of transducers 17. The board 118 has a central area clamped between the transducers 117 and the backing members 120. The board 118 has a side arranged along the side surface of the backing member 120. The plurality of signal lines 122 are formed with electrode pads. The plurality of signal lines 122 are connected to the signal electrodes 115 of the plurality of transducers 117 through the electrode pads.
In the meanwhile, the ultrasonic probe is to be used in contact with the subject as noted above. There is a necessity to design it to a surface temperature not to exceed a constant temperature in respect of safety.
Meanwhile, in the operating state of the ultrasonic diagnostic apparatus, transmission and reception of ultrasonic waves are performed from the ultrasonic transducers in the ultrasonic probe. Particularly, in ultrasonic-wave transmission, all the portion of an ultrasonic wave generated is not necessarily transmitted into the subject but a part thereof is absorbed in the ultrasonic transducer and turned into heat.
On the other hand, there is a method of increasing an ultrasonic wave output, as one approach to improve the S/N ratio of an image of the ultrasonic diagnostic apparatus. The ultrasonic wave output cannot be increased endlessly because of regulated in the upper limit. However, it if increased in the range of safety enables to obtain an image with an improved S/N ratio.
However, where ultrasonic wave output is increased, there is an increase of heat generation in the interior of the ultrasonic probe, thus being restricted in surface temperature.
For example, in a two-dimensional ultrasonic probe, there are a greater number of transducers than those in the one-dimensional probe. This results in an increase of heat generation. There is a tendency of greater difficulty in preventing the surface temperature from exceeding a constant level.
In JP-A-2001-309493 proposed by the present inventors aiming at proposing a method of extending the signal lines respectively provided for transducers each, an ultrasonic probe is disclosed which is made in a two-dimensional array by stacking a plurality of ultrasonic transducer units wherein one ultrasonic transducer unit is made by the transducers in one row.
However, in a two-dimensional probe array structured by stacking a plurality of ultrasonic transducer modules as in the invention described in JP-A-2001-309493, the signal-line extension pattern of from the transducers is structured to pass the interior of a backing member. This allows the heat generated in the transducer and backing member to conduct the signal lines 31, thus being released to the exterior of the ultrasonic transducers to some extent. Heat-dissipation effect is not obtained sufficiently through the sole signal lines 31.
The backing member, in frequent cases, uses a mixture of rubber-based resin or the like. In the general cases, the heat conductivity is approximately 0.2 W/mK-10 W/mK.
On the contrary, in the material Cu (400 W/mK) and Al (230 W/mK) generally considered high in heat conductivity, there is a difference that the heat conductivity is several tens to several hundreds greater than the heat conductivity of the backing member.
There are many requirements, such as acoustic impedance, acoustic attenuation factor and workability, for the backing member. There are no cases of using the general high-heat-conductive material as in the foregoing.
However, in the case the high-heat-conductive material is in a very thin sheet form, its acoustic effect becomes less. It can be buried in the backing member.
Accordingly, in the signal lines 31 disclosed in JP-A-2001-309493, when provided in a thickness of approximately 0.02 mm, a width of approximately 0.05 mm and a line count of approximately 30-120 (not shown), the sectional area if totalized is approximately 0.12 mm2 in maximum. This, if heat conductivity is taken into account, corresponds to an increase of 50 mm2 in the backing member sectional area. Those are the components not ignorable in heat design.